Purification of ionic solutions by imbibition into and mechanical expulsion from ion-exchange material



United States Patent O PURIFICATION F IONIC SOLUTIONS BY IMBIBI- TIONINTO AND MECHANICAL EQULSION FROM ION-EXCHANGE MATERIAL Malcolm R. J.Wyllie, Indiana Township, Allegheny County, Pa., assignor to GulfResearch Development Company, Pittsburgh, Pa., a corporation of Dela-Ware Filed Jan. 19, 1956, Ser. No. 560,186

v13 Claims. (Cl. 210-33) This invention relates to method and means ofremoving ionized solutes from water and has particular reference to thepurication of water containing in solutions ionized compounds,especially when such compounds are in low concentration.

In most circumstances improved distillation means are most practicableto employ in obtaining Water free of dispersoids or solutes. In someinstances, however, the size of the installation and the degree ofpurification required render it uneconomical to use even the moreadvanced means of distillation.

My invention consists of a quite different method and means ofseparating dissolved and at least partially ionized, i.e., at leastweakly ionized, compounds from solution and briey stated comprisesbringing a solution containing an at least partially ionized solute intocontact with an ion-exchange resin gel, which swells in contact with thesolution and absorbs solvent from the solution,

draining the surficial solution away from the ion exchange material, andthereafter squeezing the swollen ion-exchange material by a forcesupplied thereto Aand expressing from said material a solution ofsubstantially reduced concentration of solute. The ion exchange resingels, which swell in contact with aqueous solutions and at the same timeremain coherent and fairly permeable, are insoluble, infusible syntheticorganic polymerio matrices having dissociable ionic groups chemicallybonded thereto and having water in gel relationship therewith. Moregenerally the ion-exchange resin is an insoluble polyelectrolyte gelwhich can exchange ions when they are in solution. My invention isadaptable for use with small presses as for example in sea rescue kitsand is also applicable to plant size installations. Each or any of theseapplications of the method and means of my invention can be mostprotably employed in a multiple system in which a partially purifiedliquid is subjected to several repetitions of the process until adesired degree of'purity is obtained. My method and means are especiallyuseful in water purication.

In the patent drawing which is supplied for the purpose of illustratingthe invention,

Fig. 1 is a schematic ow diagram in front elevation showing a two-stageinstallation for the preparation of solutions having a reduced contentof ionizable compounds, and

Fig. 2 is a diagram of laboratory apparatus in which results obtainableby employing my process are illustrated and described in speciiicexamples in the specification and which further illustrate thefundamental combination of equipment applicable to all such situations,either hand presses or plant size installations.

My invention is also applicable to the function of increasing theconcentrations of ionizable compounds in water in which case multiplestage processes can again be used until the desired increase inconcentration of ionizable compounds in the water has been obtained.

Referring more particularly to Fig. 1 an aqueous solumaximum volume, the

ice

tion of ionizable compounds is fed through line 10 into feed tank 11.Solution from feed tank 11 is pumped by pump 12 through Iline 13 andline 14 into mixer 15 which is supplied with mixing means 16. A hopper17 containing dried, conditioned ion-exchange resin is dis.

, settler 19 through line 20.

'Ihe settled slurry from settler 19 is pumped by a pump 21 through line22 into a continuous centrifuge 23. Aqueous solution that clings to thesurface of the ionexchange resin is removed in the said centrifuge 23and flows from the centrifuge through line 24 to juncture with line 20whence the mixed elfluents can be directed to waste. In operationshaving the purpose of concentrating ionic solutions, the eflluent inline 20 would be directed to -another stage of the process and intocontact therein with a further quantity of ion-exchange material.

Ion-exchange resin which is apparently surface dry flows from thecentrifuge 23 and is conveyed by conveyor means 25 into a press 26containing, for example, a screw of decreasing pitch 27 that is operatedby the motor 28. As the ion-exchange resin is moved by the said screw 27in the direction of the arrow indicated on the drawing it is broughtunder an increasing squeeze pressure. During the time that theion-exchange material is iirst squeezed in the press, the waterexpressed by this squeezing action is withdrawn through line 30 by pump31 and is pumped thereby through line 32 into a second'mixed 33 having amixing means 34 and being substantially identical to the aforesaid mixer15.

jected to a much higher squeeze pressure by the remainder Consequentlythis liquid is flowed from the press 26 through line 35 to means forstoring or utilizing thel product.

Ion-exchange resin which has dryness in the press 26 and which has beenrestored to substantially its original volume is removed from the press26 by means 36 and is passed by means 37 and 40 l.

into the hopper 17 from which it can be withdrawn for Water ofconsiderably reduced concentration of ionizable compound isintroducedvthrough line 32 into the said mixer 33. Ion-exchange resinthat is delivered from `a source, not shown, through a line 42 into ahopper 43 is then added to the terial has been accomplished `and thematerial, as deter.- mined by prior test,

entire mixture is withdrawn from the mixer 33 through line 44 intosettler 45 in which a thick slurry of water and ion-exchange resinsettles and from which can be rdecanted a solution containing a .i

slight increase in concentration of ionizable compound. The decantedliquid is withdrawn' through line 46 and is pumped by pump 47 throughline 48 into feed tank 11.

In many instances, of course, there will be insuicient' value in thewater withdrawn Afrom settler 45 to warrantA its retreatment and it maywell be discarded, but as it-A will have a concentration of ionizablecompounds slightly;

Patented May 30, 1961' The ion-exchange resin in the press 26 is thensub-Y been squeezed to .partial 'i n solution in the mixer 33. Afterthorough ymixing of the water and the ion exchange ma@ has swollen toapproximately its'v less than that of the feed stock, in some instancesit will be proiitable to recycle it.

Settled slurry of ion-exchange resin and water are pumped by pump 50from the settler l45 through line 51 and through line 52 into acontinuous centrifuge 53. A substantial amount of the Water which clingsto the surface of the ion-exchange resin is separated in the centrifuge53. This so-separated water ilows through line 54 to juncture with line46 and into adrnixture with the decanted Water from settler 45.

Partially dried ion-exchange resin is withdrawn from the centrifuge 53by means 55 fand is introduced into a press 56 having screw 57 `andmotor 58, said press, screw and motor being of substantially the samedesign as that of press 26, screw 27 and motor 28. Press 56 is also atwo-stage press, and, `from the iirst stage Where a lower squeezepressure is employed, a liquid is Withdrawn through line 59 intojuncture with line 35 and this mixed liquid can be tlowed either to `anadditional stage of ion exchange treatment (not shown) or to means forstorage of utilization of the produce liquid. Liquid from the seconestage of the press 56 which has been subjected to a higher squeezepressure is flowed through line |60 from the press 56 and can bedirected either to additional means or to an additional stage of ionexchange treatment or can be sent to storage or means lfor utilizationof the liquid.

Squeezed and partially dried ion-exchange resin is removed from thepress 56 and carried by means 61 to storage means 62. The ion-exchangeresin, which has been restored to substantially its original volume, ispassed yfrom storage 62 by means 63 to the hopper 17 or can be directedby means 64 to the hopper '43 `for reuse either in the `first or secondstage of the process.

A plan such as has been described above and illustrated in Fig. l iscapable of treating 100 mixer volumes per day of -water containing about11,000 parts per million of salt and supply the same through line 60 aspotable drinking Water and through line 59 as Water suitable -for manyindustrial or domestic purposes.

Reference is now made to Fig. 2 which illustrates a specific example ofmy method and means as employed in the deionization of -a 0.48 normalaqueous sodium chloride solution. A cylinder 65 is charged with a drynuclear sulfonic cationic exchange resin manufactured by Dow ChemicalCompany and having the trade name Dowex-SO. Bauman, Skidmore, and Osmun(Industrial and Engineering Chemistry 40, page 1350 (1948)) defineDoWex-SO as a cation-exchange resin with a crosslinked aromatichydrocarbon chain containing nuclear sulfonic acid .groups as the solecation active group. U.S. Patent No. 2,566,353 to Mills, issuedSeptember 4, 1951, defines Dowex-SO as a sulfonated polystyrene. 'I'hesize distribution of ADoWex-SO is as follows:

TABLE I Wet mesh analysis of Dowex-SO in sodium form as shipped Percentn ZO-meslL 50.0 On l30mesl1 35.0 On l0-mesh 12.0 On Sil-mesh 2.5 O11 pan0.5

4 The top of the charge is defined by piston 72 shown in solid lines ina Withdrawn position.

After approximately 5 volumes of salt solution have been passed throughthe cylinder -6'5 and expelled through line 70, valves 69 and 71 areclosed thus preventing further iiow of salt solution through thecylinder. Aqueous solution which has been discharged through line 70will be slightly increased in salt concentration over feed solution.

The passage of several volumes of salt solution through the cylinder isAdesirable so that the salt concentration in the suriicial water on theresin particles will be reduced to a level at least approaching theconcentration of the inuent solution. This in turn is advantageous forthe reason that the salt concentration of the initial increments ofWater squeezed from the ion-exchange resin will approximate that in thesuriicial solution remaining on the ion-exchange resin particles. Inpractice l have `found that after approximately five volumes of saidsolution have been passed through the compression chamber, the normalityof the effluent solution, and therefore that of the solution on thesurfaces of the particles, will be ap-V proximately equal to thenormality of the influent solution. Ordinarily this aqueous sodiumchloride solution is discarded; it can, however, be recycled to line 68yfor the extraction of more desalted water therefrom. In a systemdirected to the provision of a more concentrated solution, eiliuent fromvalve 71 would be passed through several additional beds of partiallydry ion-exchange resin until the desired concentration is reached.

Cylinder `65 is also supplied with air inlet line 73 having disposedtherein valve 74, which inlet line feeds into an upper portion ofcylinder -65 at a point below the piston 72 in its upper retractedposition. The cylinder 65 is also supplied with an outlet line 75 havingdisposed therein a valve 76 which line leads from the bottom of thecylinder to juncture with line 77 having disposed therein valve 78, andline 79 having disposed therein valve lS0. As soon as valves 69 and 71have been closed Valves 76 and 78 are opened and salt solution stillpresent in the cylinder is drained therefrom through lines 75 and 77,valve `80 in line 79 being kept closed during this operation.

An air blast is then directed `from a source (not shown) through line 73into the chamber of the cylinder I65, the air being expelled throughopen lines 75 and 77. This blast of air serves to remove physicallysurface water from the ion-exchange material. When the cylinder has beencompletely 'ushed with air, valve 74 is closed and piston 72 is loweredunder pressure until the bed of ion-exchange material in the cylinder 65has been compressed into a space, deined by the perforated plate, thecylinder and the piston that is 61.5 percent of original volume. In thisspecific example the cylinder 65 is of such volume that 4.4 gallons ofaqueous solution are obtained by the compression step; this solutioniiows from fthe cylinder through open lines 75 and 77. The averagenormality of this solution is 0.45 although the last portionso-expressed will have a normality of 0.37.

At this point valve 78 is closed and valve 80 is opened. The piston 72is then lowered under further pressure until the resin bed is compressedinto a space defined by the perforated plate, the cylinder, and thepiston that is 53 percent of original volume and 4.4 gallons of aqueoussalt solution having a normality of 0.18 are expressed. This solutionflows through open lines 76 and 80 into sump 81. Upon the completion ofthis step valves 80 and 76 are closed, piston 72 is retracted to itsoriginal position and the above described cycle is repeated.

As soon as a sufficient volume of solution is collected in sump 81,solution is withdrawn therefrom through line S2 and is pumped by pump 83through line 84,

having disposed therein opened valve 85, into a second cylinder y86.Solution may be continuously withdrawn from the sump 81 during thecycles of ushing operations in cylinder 86.

essais Solution entering the chamber of cylinder 86 iowsY upwardly incontact with a bed of ion-exchange resin supported on perforated platel87 and flows out of the chamber through line 88 in which is disposedopen valve 89. The bed of dry ion-exchange resin in cylinder 86 fillsthe cylinder from the perforated plate `87 to a point about 3A thedistance from the plate 87 to the face of a piston 90 in its retractedposition as shown in solid lines in Fig. 2.

As soon as a volume of liquid substantially equal to 5 times the volumeof the chamber of cylinder 86 has been passed therethrough, pumping ofsolution from the sump 81 is discontinued -and valves 85 and 89 areclosed. The liquid which during this operation has owed from line 488can be discarded to waste or recycled either to the supply line `68 orto the solution in sump 81. Valve 91 in air line 92, valve 93 in outletline 94 and valve 95 in line 96 are then opened and air is blasted intothe chamber of the cylinder 86 to remove physically surface liquid fromthe ion-exchange resin. Valve 97 in line 98, which extends from juncturewith lines 94 and 96, is kept closed during this'operation. Solutionwhich is removed by the air blasting step and which has a normality ofabout 0.18 or slightly higher can be discarded or can be recycled tosolution inlet line 68 or the sump 81.

Upon completion of the air flushing step, valves 91 and 95 are closedand valve 97 in line 98 is opened. Piston 90 is then lowered until thespace occupied by the chamber of cylinder 86 is reduced in volume to 50percent of the former volume. During this compression 1l gallons of asolution having an average normality of 0.09- is caused to ow throughopen lines 94 and 98 into the sump 99. The solution as it Hows to sump99 during the compression by piston 90 will vary in normality from aninitial 0.18 to a last drop normality of 0.004. The second-stageapparatus can be operated with a plurality of compressing vessels (notshown) and a portion of the expressed liquid can be separated from theremainder so that aqueous salt solutions having a selected concentrationbetween the average normality of 0.09 and a last drop normality of 0.004can be obtained. Thus even with a two-stage operation aqueous solutionof sodium` chloride can be sufliciently reduced in concentration torender the water useful for most purposes.

In another speciic example of operation according to my invention toreduce the salt content of water, an anion exchange resin was employed.Particles of a strongly basic-quaternary alkanolamine-type anionexchange resin in the chloride form was conditioned in a solution ofcaustic and then treated to restore the chloride form. The sizedistribution of this anion exchange resin was as follows:

TABLE II Wet screen analysis (U.S. standard screens) Size of mesh:Percent retained Fines content: Less than 2%.

, 6 move surlicial water theret'ro was removed and the water content ofthe equilibrated resin was determined-to be 1.419 grams of water pergramofr resin. The remainderoffthe equilibrated resin was introducedinto a metal cylinder and subjected to the pressure of a piston. Samplesof expressedwater were taken for each 1A inch movement of the piston andabout 1.6 milliliters of water were expressedvfor each increment, afterthe first increment, of piston movement. After l12 samples .had beentaken and the -bed of anion exchange resins was proportionatelyvcompressed, the pressure on the bed of anion exchange resin was 15,000pounds per square inch. The total volume of expressed liquid was 20.1milliliters and the average normality of the expressed liquid was 0.117.It was determined that the foregoing process expressed 99% of the saltcontent of the resin and 60% of the water content. The single step thusperformed reduced the salt concentration of the treated solutiontorone-half itsy original concentration. It can lbe seen also thatfurther compression of the resin would yield an even more dilutesolution inasmuch as 99% of the salt has already been removed. Inaddition separation of the different portions of expressed water fromthe above single cornpression step can yield solutions of much reducedaverage salt concentration. For example, the underlined numbers showthat one-half of the expressed water if so separated will have a saltconcentration of about one-quarter of that of the feed solution.

Cumulative Avg. Norm. (MgCl2) Cum. Rev. Avg. Norm. (MgCl2) Reverse CurnVol.,

Percent Volurne, ml.

Normality (MgCl2) Increment No.

Generally speaking, either a synthetic cation or anVv anion exchangeresin lgel can be employed with equal facility in obtaining solutions ofincreased or decreased salt concentration from a feed stock saltsolution or, more speciiically, in the desalting of water. The fact thatso many synthetic ion-exchange resins are cornmercially available makesit possible to select a resin tailored to the speciiic ions and ionconcentration of the solution to be treated. Thus a Igel with highcrosslinking and low Water content Will yield on compression fresherwater than a gel containing the same number of ion-exchange -groups onthe matrix but having a lower degree of crosslinking. Conversely,however, more water can be obtained at the same pressure yfrom a resinof lesser crosslinking. However it is also within the scope of myinvention to select, for purposes of enhanced efficiency in treatment,an anion exchange resin when the anion of the solution is of large ionicvolume or a cation exchange resin in the opposite case. It isfurthermore within the scope of my invention to combine in the treatmentof solutions, beds of mixed cation and anion exchange resins, or, in thecase of treatment in series, as shown in the drawing, an anion exchangeresin can be used in one cylinder and a cation exchange resin inanother.

Having described my invention I claim:

l. A process of separating a solution of an at least partially ionizedsolute in a solvent that is ionized to A sample of the resin'centration,4 the saidpro'cess comprising: bringing an at* leastpartially dry synthetic vion-'exchange resin andsolution that contains asubstantial proportion of ionized solute into contact with one another;separating unabsorbed solution from the saidtion-exchange resin aftersolution and resin have been in contact at least long enough to permitthe resin to absorb solvent from the solut-ion, the so-separatedsolution constituting the portion'of increased solute concentration; andsubjecting the ion-exchange resin to mechanical pressure so .as toexpress absorbed solution from the said resin, the soexpr'essed solutionconstituting the solution of decreased solute concentration.

2. The process of claim 1 in which the lion exchange resin is acation-exchange resin.

3. The process of claim 1 in which the ion exchange resin is ananion-exchange resin.

4. The process of claiml 1 in which the solution is aqueous and thesolute is a compound that is soluble and ionizable in water.

5. A process of separating at least partially yionized aqueous saltsolution into a solution having a decreased salt concentration andanother solution hav-ing an increased salt concentration, the saidprocess comprising: bringing a feed aqueous salt solution that containsa substantial proportion of an ionized salt into contact with asubstantially dry synthetic ion exchange resin lgel and maintaining saltsolution in contact with the said resin for a sufficient period topermit the said resin to absorb a solution of decreased concentrationfrom the feed solution; separating unabsorbed salt solution of increasedconcentration from contact with said ion exchange resin; and expressing,by imposing mechanical pressure upon the so-treated ion-exchange resin,absorbed aqueogun solution from the resin having a decreased saltconcentration.

6. The process of claim 5 in which the said resin is Y continuouslybrought into contact with Athe said resin and is, except for thatportion which is absorbed by the resin, continuously withdrawn fromcontact therewith.

8. The process of claim 5 in which the ionizable groups attached to thematrix of the ion exchange resin are of` the same sign of charge as anion ofsubstantial: concentration in solution which has the largest ionicvolume of the ions in saidsolution. f I '9. A process of removingsoluble salt from water containing a substantial proportion of thesame-in solution, said salt being in at least partially ionized form,said process comprising: bringing such feed solution into contact with apreviously substantially dried synpressure upon the resin, absorbedWater therefrom in a plurality of separately collected increments andincreas-` ing the pressure upon said resin while expressing saidincrements, solution expressed under 'the most elevated j pressurehaving the lowest salt concentration.

10. The process of claim 9 in which an increment so- 'i expressed underpressure is recycled to form feed solu- Ition to the ion-exchange resin.

11. The process of claim 9 in which compressed ionexchange resin is,after expression of absorbed water, Vdried and recycled to the contactof additional feed stock solution. 12. The process of claim 9 in whichthe synthetic resin is an anion-exchange resin.

13. The process of claim 9 in which the synthetic resin is acation-exchange resin.

References Cited in the file of this patent UNITED STATES PATENTS1,705,908 De Witt Mar. 19, 1929 2,296,897 Billing et al. Sept. 29,V 19422,678,132 Beard May 11, 1954 2,684,331 Bowman July 20, 1954 2,696,305Slover Dec. 7, 1954 2,771,193 Simpson Nov. 20,

OTHER REFERENCES Simpson and Bauman: Concentration Effects of Recyclingin Ion Exclusion, 46, Industrial and Engineering Chemistry, 1958-1962(1954)` Wheaton and Bauman: Ion Exclusion, 45, Industrial andEngineering Chemistry, 228-233 (1953).

9. A PROCESS OF REMOVING SOLUBLE SALT FROM WATER CONTAINING ASUBSTANTIAL PROPORTION OF THE SAME IN SOLUTION, SAID SALT BEING IN ATLEAST PARTIALLY IONIZED FORM, SAID PROCESS COMPRISING: BRINGING SUCHFEED SOLUTION INTO CONTACT WITH A PREVIOUSLY SUBSTANTIALLY DRIEDSYNTHETIC ION-EXCHANGE RESIN GEL FOR A PERIOD SUFFICIENT FOR THE SAIDRESIN TO ABSORB WATER CONTAINING A LESSER CONCENTRATION OF SALT THANTHAT OF THE SAID FEED SOLUTION; SEPARATING UNABSORBED FEED SOLUTION FROMTHE SO-TREATED RESIN; AND EXPRESSING, BY THE APPLICATION OF MECHANICALPRESSURE UPON THE RESIN, ABSORBED WATER THEREFROM IN A PLURALITY OFSEPARATELY COLLECTED INCREMENTS AND INCREASING THE PRESSURE UPON SAIDRESIN WHILE EXPRESSING SAID INCREMENTS, SOLUTION EXPRESSED UNDER THEMOST ELEVATED PRESSURE HAVING THE LOWEST SALT CONCENTRATION.
 11. THEPROCESS OF CLAIM 9 IN WHICH COMPRESSED IONEXCHANGE RESIN IS, AFTEREXPRESSION OF ABSORBED WATER, DRIED AND RECYCLED TO THE CONTACT OFADDITIONAL FEED STOCK SOLUTION.